HASKELL help

Please provide a brief explanation of why the answer is what it is and why the other choice is incorrect.

Consider the Haskell code snippet "a= a + 1". Which of the following options is 1 point correct with regards to this snippet? * This is not valid Haskell syntax This is valid Haskell syntax, which compiles without error, and increments the value of a This is valid Haskell syntax, which compiles without error, but does not increment the value of a